The invention relates to a camshaft adjuster for an internal combustion engine. Such camshaft adjusters are used to adjust the relative angular position between a driving element, such as a driving wheel, which is in driven connection with a crankshaft of the internal combustion engine via traction element, such as a chain or a belt, and a driven element driving a camshaft. In this way control times of valve movements of the internal combustion engine are changed, for example, for improving the emission values, the fuel consumption, and the power profile. Such camshaft adjusters have a locking unit with a locking element, which produces a positive-fit connection between the driving element and the driven element in a locked operating position. In this way, in partial operating ranges of the internal combustion engine, for example, when the internal combustion engine is started or there is a drop in hydraulic pressure or there is a constant power demand, a set angle of the camshaft adjuster is fixed.
For example, due to times that the motor is stopped, it can occur that the camshaft adjuster is no longer completely filled with oil. After restarting the internal combustion engine, under some circumstances it takes a few seconds until the adjuster is completely filled with oil again. In this transition time, the absence of a locking unit can lead to control problems in the phase reference between the crankshaft and camshaft. This can cause worse exhaust-gas values and/or power values and can have negative effects on the service life and noise generation.
From the publication DE 197 55 497 A1, a camshaft adjuster with a vane-cell construction is known, in which the driving element is firmly connected to the driving wheel, while the driven element is connected rigidly to the camshaft. The driven element carries a piston, which is acted upon on one side by a spring and upon which a hydraulic force acts in the opposite direction. For a drop in hydraulic pressure below a threshold set by the spring, the spring moves the piston in the direction of the driving element, so that the piston enters into a corresponding recess of the driving element with a projection in the circumferential direction, forming a positive fit, which achieves a locking effect. The adjustment movement is here oriented in the axial direction of the camshaft adjuster.
From the publication DE 199 83 890 T1, a locking mechanism is known, with which a rotational movement of a driven element relative to a driving element can be limited. With this locking mechanism, a radial movement of a locking element takes place.
From the publication DE 197 24 989 A1, a construction of a camshaft adjuster is known, in which the driving element has external helical gearing and also the driven element has internal helical gearing and an adjustment element that can move axially depending on the action of a hydraulic force engages with the two helical gearings noted above for generating an adjustment movement. The driven element carries a spring-loaded hydraulic piston, which can move axially and which has radial gearing that can be brought into corresponding gearing of the driven element in the locked operating position in the axial direction.
In an alternative embodiment of publication DE 195 41 769, locking is realized not between the driving wheel and camshaft, but instead between the adjustment element noted above, which in this case forms the driven element in the sense of the invention, and driving element locked in rotation with the driving wheel. For this locking, the adjustment element has a projection, which can be displaced hydraulically in the radial direction and which can enter into a corresponding recess of the driving element.
From publication DE 196 23 818 A1, a camshaft adjuster with a vane-cell construction is known, in which a locking pin that can move axially, is spring loaded, and can be pressurized hydraulically in the axial direction into a vane formed with the driving element. In the locked operating position, the locking element constructed as a locking pin with a cone enters into a corresponding recess of the driven element in the axial direction. A guiding ring, which is to influence the guiding and sliding properties between the locking element and the driving element, is connected loosely between the driving element and the locking element.
Additional state of the art in terms of locking elements are known, for example, from publications DE 196 30 662 A1, DE 197 00 866 A1, DE 197 23 945 A1, DE 197 16 203 A1, DE 197 00 866 A1, DE 100 36 546 A1, DE 199 61 193 A1, DE 100 39 923 A1, DE 100 31 974 A1, and DE 100 55 334 C2.
From publication WO 03/076771 A1, it is known to produce components of the camshaft adjuster from a high load bearing, non-metallic material with at least one high load bearing plastic, by means of which advantages in terms of cost and energy are to be achieved. The high load bearing, non-metallic materials should be produced from one part or integrally for parts of the adjustment assembly, driving wheel, stator, covers, and sealing rings. Insert parts, such as screws, nuts, sleeves, and seals, and the like can be injection molded in the high load bearing plastic, wherein threading should also be cut or injected molded directly in the plastic.